Adiabatic potential energy surfaces for the (2)A(＇) and (2)A(＇) states of the Ar(S-1)-OH(X(2)Pi) complex were calculated using supermolecular unrestricted fourth-order Moller-Plesset perturbation theory and a large correlation consistent basis set supplemented with bond functions. The potential energy surface (PES) of the A(＇) state has two minima. The global minimum from the unrestricted coupled-cluster calculations with single, double, and noniterative triple excitations occurs for the collinear geometry Ar-H-O at R=7.08a(0) with a well depth of D-e=141.2 cm(-1). There is also a local minimum for the skewed T-shaped form, whereas the Ar-O-H arrangement corresponds to a saddle point. The PES of the A(＇) state also has two minima, which occur for the two collinear isomers. A variational calculation of the bound rovibrational states was performed. The calculated binding energy, D-0=93.8 cm(-1), and the energies of the bound vibrational states are in good agreement with experiment [see Berry , Chem. Phys. Lett. 178, 301 (1991) and Bonn , J. Chem. Phys. 112, 4942 (2000), preceding paper]. (C) 2000 American Institute of Physics. [S0021-9606(00)01211-3].